Yaoxing Liu

Electrochemical removal of chromium from aqueous solutions using electrodes of stainless steel nets coated with single wall carbon nanotubes

An electrochemical technique was adopted to investigate the removal of Cr(VI) species and total chromium (TCr) from aqueous solution at a laboratory scale. The electrodes of stainless steel nets (SSNE) coated with single wall carbon nanotubes (SWCNTs@SSNE) were used as both anode and cathode. Three parameters, including solution pH, voltage and electrolyte concentration, were studied to explore the optimal condition of chromium removal. The optimal parameters were found to be pH 4, voltage 2.5 V and electrolyte concentration 10 mg/L. Under these conditions, the Cr(VI) and TCr removal had a high correlation with the amount of SWCNTs coated on the electrodes, with coefficients of the regression equations 0.953 and 0.928, respectively. The mechanism of Cr(VI) removal was also investigated. X-ray photoelectron spectroscopy (XPS) study and scanning electron microscope (SEM) picture showed that the process of chromium removal involved the reduction of Cr(VI) to Cr(III) on the cathode, and then the adsorption of Cr(III) by SWCNTs on the cathode. The study results indicated that the proposed method provided an interesting means to remove chromium species from aqueous solution, especially Cr(VI) in acidic condition.

Reverse flow injection analysis method for catalytic spectrophotometric determination of iron in estuarine and coastal waters: A comparison with normal flow injection analysis

A method for determining iron in seawater had been developed by coupling reverse flow injection analysis (rFIA) and catalytic spectrophotometric detection with N,N-dimethyl-p-phenylenediamine dihydrochloride (DPD). With a seawater sample or a standard solution as the carrier, the mixture of DPD and buffer was injected into the carrier stream quantitatively and discretely. After mixing with H(2)O(2), the DPD was oxidized to form two pink semiquinone derivatives that were monitored at 514 nm wavelength with a reference at 700 nm. The method detection limit was 0.40 nmol L(-1), lower than half of that of normal flow injection analysis (nFIA) method. The sample throughput was 10h(-1) with triplicate determination, compared with 4h(-1) for nFIA-DPD method. The analysis results of the certified seawaters CASS-4 (12.33 ± 0.18 nmol L(-1)) and NASS-5 (3.47 ± 0.23 nmol L(-1)) well agreed with the certified values (12.77 ± 1.04 and 3.71 ± 0.63 nmol L(-1), respectively). The typical precision of the method for a 2.97 nmol L(-1) iron sample was 4.49% (n=8). Interferences from copper and salinity were investigated. An instrument was assembled based on the proposed method and applied successfully to analyze total dissolvable iron (TDFe) in surface seawater samples collected from the Pearl River Estuary, the results of which revealed non-conservative behavior of TDFe during the estuarine mixing. Results for these samples with both rFIA-DPD and nFIA-DPD methods showed good agreement with each other. The proposed method was superior to the currently used nFIA-DPD method, particularly when it is adapted for field and in situ deployment, due to its lower reagent consumption, higher sample throughput and keeping the manifold tubing clean.

Mercury distribution in seawater discharged from a coal-fired power plant equipped with a seawater flue gas desulfurization system.

Background and purposeMore and more coal-fired power plants equipped with seawater flue gas desulfurization systems have been built in coastal areas. They release large amount of mercury (Hg)-containing waste seawater into the adjacent seas. However, very limited impact studies have been carried out. Our research targeted the distribution of Hg in the seawater, sediment, biota, and atmosphere, and its environmental transportation.MethodsSeawater samples were collected from five sites: 1, sea areas adjacent to the power plant; 2, near discharge outlets; 3, the aeration pool of the power plant; and 4 and 5, two reference sites. The total gaseous Hg was determined in situ with a Tekran 2537B. Analyses of total Hg (TM) followed the USEPA methods.ResultsIn most part of the study area, TM concentrations were close to the reference values and Hg transfer from the seawater into the sediment and biota was not obvious. However, in the aeration pool and near the waste discharge outlets, atmospheric and surface seawater concentrations of TM were much higher, compared with those at a reference site. The concentration ranges of total gaseous Hg and TM in seawater were 3.83–8.60xa0ng/m3 and 79.0–198xa0ng/L near the discharge outlets, 7.23–13.5xa0ng/m3 and 186–616xa0ng/L in the aeration pool, and 2.98–4.06xa0ng/m3 and 0.47–1.87xa0ng/L at a reference point.ConclusionsThis study suggested that the Hg in the flue gas desulfurization waste seawater was not only transported and diluted with sea currents, but also could possibly be transferred into the atmosphere from the aeration pool and from the discharge outlets.

Effects of metabolites of benzo(a)pyrene on unschedule DNA synthesis in BALB/3T3 cell line.

In order to explore the damage from metabolites of benzo(a)pyrene on DNA of mammalian cells, the effects of four metabolites of benzo(a)pyrene (anti-BPDE, syn-BPDE, 3-OH-BP and 9-OH-BP) on synthesis of DNA and unschedule DNA synthesis (UDS) in BALB/3T3 cells were assayed, by methods of single-labeling and double-labeling. The results showed that all of the four agents were able to increase the synthesis of DNA, but only three of them (apart from syn-BPDE) induced UDS in BALB/3T3 cells. The above indicates that the metabolites of benzo(a)pyrene are able to damage DNA in BALB/3T3 cells, and that this effect may be relative to the sterical structure of metabolites of benzo(a)pyrene.

Temperature effects on arsenate adsorption onto goethite and its preliminary application to arsenate removal from simulative geothermal water

Laboratory batch experiments were conducted in order to assess the impacts of temperature on the performance of goethite in removing arsenate from water. All batch experiments were conducted at four temperatures (30, 50, 70 and 90 °C) and pH 4.6. The results showed that both the arsenic uptake rate and capacity were significantly enhanced with increasing temperature from 30 to 90 °C. The adsorption kinetics followed a pseudo-second-order model with coefficients of determination (R2) all above 0.999. The process followed the Langmuir model, and several thermodynamic parameters were calculated. Arsenate adsorption was facilitated more under simulative geothermal water conditions than in RO (reverse osmosis) water. The crystalline structure of goethite was not changed after adsorption at various temperatures. XPS results showed a decrease in the content of iron hydroxyl groups, which demonstrated that arsenate adsorption onto goethite may be realised through the replacement of the iron hydroxyl group to form inner-sphere bidentate/monodentate complexes at pH 4.6.

Electrochemical disinfection using a modified reticulated vitreous carbon cathode for drinking water treatment

A reticulated vitreous carbon (RVC) cathode modified by anodic polarization in 20u202fwt% H2SO4 solution was used for drinking water disinfection under a neutral low electrolyte concentration (0.25u202fg/L Na2SO4) condition. The contribution of the modified RVC anode and the Ti/RuO2 cathode to disinfection was investigated. The influences of current, initial Escherichia coli load, temperature and water volume were studied. The results show that H2O2 generation increased to approximately three times using the modification of the RVC. E.xa0coli was mainly deactivated by the H2O2 generated at the cathode. For water with about 106u202fCFU/mL E.xa0coli, the detection limit (<4u202fCFU/mL) was reached under different conditions. Increasing current could simultaneously shorten the treatment time and increase the energy consumption (EC) simultaneously. Although decreasing the initial load reduced the treatment time, the EC for per log E.xa0coli removal increased. The time required for disinfection shortened from 3.5 to 2.5u202fh and the EC for per log removal decreased from 218.5 to 123.2u202fWh/m3 when the temperature increased from 20 to 40u202f°C. Although more time was required for disinfection, the EC decreased from 218.5 to 141.4u202fWh/m3 when the volume was doubled.

High-load domestic wastewater treatment using a combined anaerobic-aerobic bio-filter with coal cinder as medium

ABSTRACT A combined anaerobic-aerobic bio-filter technology was used for field treatment of high-organic-load domestic wastewater with coal cinder as the bio-filter medium. The effects of parameters, including hydraulic retention time (HRT) and backflow ratio, on the decrease in the chemical oxygen demand (COD), NH3-N, total nitrogen (TN), total phosphorus (TP), and turbidity were investigated. The results showed the obvious influence of the HRT and ratio of backflow on wastewater treatment. Under the optimal HRT condition of 18u2005h, the removal efficiencies of COD, NH3-N, TN, TP, and turbidity were 67.9%, 95.6%, 30.4%, 65.6%, and 83.8%, respectively. When the backflow ratio (2:1) was added to the treatment system, the TN removal obviously increased, and the removal efficiencies of COD, NH3-N, TN, TP, and turbidity were 88.1%, 91.7%, 69.9%, 69.6%, and 97.5%, respectively. These results indicated that the combined technology has the potential as a treatment method for high-organic-load domestic wastewater.